Did you know that bad unit test quality leads to the same problems as having no unit tests at all?
The following graphic emphasizes the importance of unit testing in general. Over time, the spent work increases dramatically while completely slowing down the progress of software development when you skip writing any unit tests at all.
In the next graph you see how little badly written unit tests improve the situation. With no unit tests, over time it is getting harder and harder to develop new functionality in a growing software solution. If your unit tests are in poor quality you can only delay this dilemma. The goal is to write good unit tests to have a steady work spent over time and adding new features stays an easy task.